California water resource region facts for kids

The California water resource region is one of 21 major geographic areas, or regions, in the first level of classification used by the United States Geological Survey to divide and sub-divide the United States into successively smaller hydrologic units. These geographic areas contain either the drainage area of a major river, or the combined drainage areas of a series of rivers.

The California region, which is listed with a 2-digit hydrologic unit code (HUC) of 18, has an approximate size of 168,579 square miles (436,620 square kilometers), and consists of 10 subregions, which are listed with the 4-digit HUCs 1801 through 1810.

This region includes the drainage within the United States that ultimately discharges into the Pacific Ocean within the state of California; and those parts of the Great Basin (or other closed basins) that discharge into the state of California. Includes parts of California, Nevada, and Oregon.

The California region, with its 10 4-digit subregion hydrologic unit boundaries.

List of water resource subregions

Subregion HUC	Subregion Name	Subregion Description	Subregion Location	Subregion Size	Subregion Map
1801	Klamath–Northern California Coastal subregion	The drainage into the Pacific Ocean from and including the Smith River Basin to and including the Stemple Creek Basin.	California and Oregon.	24,800 sq mi (64,000 km2)
1802	Sacramento subregion	The Sacramento River Basin and drainage into Goose Lake.	California and Oregon.	27,600 sq mi (71,000 km2)
1803	Tulare–Buena Vista Lakes subregion	The drainage into the Tulare and Buena Vista Lake closed basins.	California	16,200 sq mi (42,000 km2)
1804	San Joaquin subregion	The San Joaquin River Basin.	California	15,600 sq mi (40,000 km2)
1805	San Francisco Bay subregion	The drainage into the Pacific Ocean from the Stemple Creek Basin boundary to and including the Pescadero Creek Basin, excluding the Sacramento and San Joaquin River Basins.	California	4,470 sq mi (11,600 km2)
1806	Central California Coastal subregion	The drainage into the Pacific Ocean from the Pescadero Creek Basin boundary to and including the Rincon Creek Basin.	California	11,400 sq mi (30,000 km2)
1807	Southern California Coastal subregion	The drainage within the United States that discharges into the Pacific Ocean from the Rincon Creek Basin boundary to the California-Baja California international boundary.	California	11,100 sq mi (29,000 km2)
1808	North Lahontan subregion	The drainage east of the Sierra Nevada and north of the Truckee River Basin which includes the Lahonton closed basins that discharge into California.	California and Nevada.	4,480 sq mi (11,600 km2)
1809	Northern Mojave–Mono Lake subregion	The Closed Desert Basins that discharge into South Central California, including Mono Lake, Owens Lake, Death Valley, and the Upper Mojave Desert.	California and Nevada.	28,000 sq mi (73,000 km2)
1810	Southern Mojave–Salton Sea subregion	The closed desert basins in Southeastern California, including the Lower Mojave Desert and the Salton Sea.	California	16,000 sq mi (41,000 km2)